Rocket propulsion method



Aug. 11, 1959 D. R. CARMODY E i'AL ROCKET PROPULSION METHOD Filed Aug. 12. 1954 f OX/D/ZER INVENTORS E van A. Mayer/e Dan E. Carmody W 9 ATTORNEY products of decomposition;

United Sta p e 111., assignors to Standard Oil Conipany, Chicago, 111., a corporation of Indiana Application August 12, .1954, Serial No. 449,398 3 Claims. c1. so -35.4

This invention relates to the generation of gas.- More particularly it relates to a method of reaction propulsion by the hypergolic reaction of a nitric acid' oxidizer and a liquid fuel.

Reaction propulsion or rocket propulsion operates with a fuel system that is not dependent on. atmospheric oxygen. The fuel system may consist of asingle selfcontained propellant, i.e., mono-propellant system or it may consist of a separate fuel and a separate oxidizer, i.e., bi-propellant system.

A bi-propellantrocket carries the fuel and the oxidizer in separate tanlrs. The fuel and the oxidizer are introqueen separately and substantially simultaneously into the inbustion chamber'of the rocket motor. The gas eousproducts of the reaction of the fuel aiid the oxidizer'aiedischar'ged" through an exit nozzle; the forward thrust is developed by the passage of these gaseous prodticts'through the nozzle. A self 'igniting fuel system preferred because of the possibilities offailure when using? auxiliary methods of ignition, s c as a- Spark plug or a glow plug. A fuel which is self=igniting or spontaneously combustio'nable when contacted with an oxidizer is known as a hypergolic fuel.

Temperature has an important bearing onthehypergolic' activity of fuels. The earths surface may vary in temperature from a high of about +l25' F. to a low of about 65 F. Temperatures below about -3Qf F. are exceptional. surface-to air missiles or rocket driven aircraft must be capable of operation at temperatures on the order of =30 F.; this means that a hypergolic reaction. must take place when the temttire of the fuel andi'the oxidizer at the moment contact in the combustion chamber'are at a "temperature ofab'o'ut =36 F. High altitude tempera- ,ures-are normally on the order of. 6 5 Fu and; are to reach +100 F. An ai""air m ssu mus be cue to operate at these very iow' atmospheric tempera ture spthat is, the fuel; and the oxidizer must react hypergolically even though at the. momeiit' of initial contacting inv the. combustion chamber of the rocket motor theyare at a temperature of'aboiit 6'5.' F. or even-lower.

an s eci oi, inc invention is a method or} generating .gas by the. ypergolic reaction or a and nitric acid oxidizer. Another object as method or f 'ctioh propulsion. or rocketpropulsioh. by the use ofthehypergolic reaction.v of s fuelfand a aeid oxidizer.

-,Still anotherv pbject. is. a methbd ofi'oeliet propulsion "the use of tlie.hypergolic reaction era nitric acid ,bxid-i er. and. a. fuel which sonisiiis cpr cisne amounts ,of, hydrocarbons, particularly those hydrocarbons which -a;re;ess ential1y non-hypergol ic at ordinary temperatures. xet-anothenobjegt is a novel classbf orgaiiic compounds.

Qther objects, will become apparent-.imthe. coarsest the I "detaileddescriptioii pf'the invention.

.The novel-i composition Zamora-'1jaoxatiiiaphos xpholane. undergoes-ahypergolic reaction with .iiitric. acid oxidizers at atmospheric temperatures to. produce gaseous fuels can be used in.

7 Patented Aug. 11, 19 59 rocket propulsion by-injecting'the fuel and a nitric sci-(r oxidizer separately and substantially simultaneously into the combustion chamber of a rocket motor anddischarging the gaseous decomposition products from saidcjombustion chamber through an exit nozz'le.'

The composition of'thisinvention is hypergoli'c nitric acid oxidizersat ordinary temperatures, such about 75 At temperatures on the order of 0 F1 a hype'rgolic reaction takes place/with nitric acid jo'xi di'zers containing as much 5 weight percentof iioii I acidic materials. The non-acidic materials generally are usedfto depress the freezing point of high purity nitric acid. The mostcommon materials-are waier it self or aqueous solutions of potassium nitrate ornitrite: These non acidic materials have an adverse-influence on the hypergolic activity ofthe nitric acid andtherefoife' nitric acid containing large amounts of these materials contains 7 percent or more of N 0 very low atmospheric temperatures, i.e., below about 6 5 F., the preferred oxidizer is RFNA containingat Iea taboui l6 percent of N 0 Nitric acid oxidizers suitable for use" atfve'rylow temperatures can be obtained by mixing WFNA with various strong oxidizing acids. A suitable nitricjac'iti in V oxidizer consists of'WFNA and oleum. Oleum consists of. sulfuric acid and dissolved S0 A blend containing about. percent of WFNA and about 20 percent ofoleum containing about 10 percent of S0,, is suitable for use at temperatureson the ord r of 65 F. Blends of WFNA and alkanesulfonic acids containing notmoi'e than 4 carbon ato'rns in the alkanegroup are particularly suitable for use at very low atmos heric temperatures, For example, a blend consisting of percent WFNA and 15 percent methanesulfonic 'acidis usable at temperatures of 7 3 F.; a blend consisting of 84 percent WFNA and 16 percent ethanesulfonic acid is usable at temperaturesof 64 F. t V

It is to be understood that while all nitric acid oxidiz'e'rs are no: suitable for u e over the entire range of atmospheric temperature the term nitric acid oxidizeris intended to include those oxidizerswhich, are suitable at the desired temperatures of initial contacting of the fuel and the oxidizer.

The novel fuel of'this invention is a heterocyclic compound having the empiricalformula'GgH oSPCl. The structural formula is:

This coi'npoundis' named: 2-chloro-1,3,2-oxathiaphosn p V The oxathiaphospholane can be-blended with liquid hydrocarbons to roduce i ypergolie fuels that are useful for gas generation orrocket propulsion. ecoiio'mical fuel is obtained with an essentially nonhypergolic liquid hydrocarbon, i.e., one thafdoes iiot react with a nitric acid oxidizer'to produce a *visible flame, although gaseous products may be produced, at

ordinar'jy temperature, i.e'., at about 80 F. Examples 'of such essentially non-hypergolic liquid hydroc rbons are heptane, octane, hoary naphtha, kerosene; jet plane fuel, diesel oil, cracked naphtha, diisobutylene, propylene tetramer, and butylene trimer.

The olefin polymers made by polymerizing butylenes or;propylenes and co-polymerizing 'butylenes and propylenes are particularly suitable essentially non-hypergolic liquid hydrocarbons.

. In general, the mixed fuel of this invention consists essentially of between about 25 and 75 volume percent of the oxathiaphospholane and the remainder a liquid hydrocarbon. For operation at very low atmospheric temperatures, it is preferred to use a fuel consisting essentially of about equal volumes of an olefin polymer containing about 8 carbon atoms and n the oxathiaphospholane.

The novel composition of this invention and the results obtainable therewith are set out in the following illustrative example.

The ignition delays set out below were determined by means of an apparatus which permitted the measurement of the delay in milliseconds. (The ignition delay is dedefined as the time between the mixing of the fuel and the oxidizer and the appearance of a visible flame.) The delays were determined by cooling the fuel and the oxidizer separately to the desired temperature and introducing these into the apparatus which had also been cooled to the desired temperature. The WFNA used in the examples contained about 2 weight percent of water. The RFNA used in the examples contained about 22 weight percent of N Example I 'The apparatus consisted of a 500 ml., three-necked round bottomed flask equipped with a stirrer, a vent and an upward slanting watercooled condenser. At the upper end of the condenser was a Y tube with dropping funnels connected to the two upper arms of the Y tube.

Approximately 1.25 moles each of phosphorus trichloride and mercaptoethanol were separately added dropwise from the dropping funnels through the arms of the Y tube. As the liquids came in contact, reaction took place and the liquids entered the slanting condensed and flowed by gravity into 250 ml. of dry methylene chloride in the flask. The condenser removed some of the heat liberated in the reaction and the hydrogen chloride formed was continuously vented. During the addition (30-45 minutes) and for about 15 minutes afterwards, the methylene chloride was stirred continuously.

After addition and reaction were complete, the methylene chloride was stripped out of the reaction mixture. During this operation, a yellow-orange solid appeared in the reaction mixture. The supernatant liquid was decanted from the solid and distilled under vacuum. Approximately 16.4 grams of distillate was obtained. The reaction can be expressed by the equation:

The product was subjected to ultimate analysis. The composition was compared on the basis that the compound was 2-chloro-1,3,2-oxathiaphospholane.

The physical characteristics of the compound are:

Boiling point, C. 42-45 at 1.5 mm. Melting point Below Q F. Density, g./ml. at 21 C. 1.473.

Refractive index, 20 C. 1.5973.

The ignition delays cf this compound were determined at various temperatures as set out in the following tabulation:

Ignition Temperature Oxidizer delay,

milliseconds F WFNA-.- 43.9 65 F RFNA- 15.8

Example II In this example, blends of the oxathiaphospholane were made with diisobutylene. The diisobutylene showed no 'hypergolic activity with WFNA. at +75 F. The ignition delays were determined visually at +75 F. when dropping th fuel into WFNA.

Blend-Percent Ignition Delay Oxathiaphos- Diisobutylene pholane 100 0 Very slight.

50 slight. 30 70 slight. 10 90 no ignition.

' valve 13 which regulates the flow of gas to maintain a constant pressure beyond valve 13. From valve 13 helium is passed through lines 14 and 16 into vessel 17 and simultaneously through line 18 into vessel 19.

Vessel 17 contains the oxidizer. Helium pressure forces the oxidizer out of vessel 17 through line 21 to valve 22. Valve 22 is a solenoid actuated throttling valve. Suitable electrical lines connect valve 22 to an electrical source and operating switch (not shown) at the control panel of the aircraft. The oxidizer is passed through line 23 and injector 24 into combustion chamber 26. Combustion chamber 26 is provided with an outlet nozzle 27.

Vessel 19 contains the fuel. Vessels 17 and 19 are constructed to withstand the high pressure imposed by the helium gas. The gas pressure forces fuel from vessel 19 through line 28 to solenoid actuated throttling valve 29. Valve 2) is similar in construction and in actuation to valve 22. The fuel is passed through line 31 and injector 32 into combustion chamber 26.

Valves 22 and 29 are of such a size and setting that a predetermined ratio of oxidizer-to-fuel is passed into combustion chamber 26. Injectors 24 and 32 are so arranged that the streams of oxidizer and fuel converge and contact each other forcibly, resulting in a very thorough intermingling of the fuel and the oxidizer.

The missile is launched by activating the solenoids on valves 22 and 29. In this illustration, 4.5 lbs. of 22% RFNA are introduced into combustion chamber 26 per pound of fuel. Herein the fuel consists of volume percent of 2-chloro-1,2,3-oxathiaphospholane and 30 volume percent of diisobutylene. The oxidizer and the fuel react almost instantaneously upon contact in the combustion chamber; a large volume or very hot gas is produced in the combustion chamber, which gas escapes through orifice 27. The reaction from this expulsion of gas drives the missile toward its target.

The extremely good ignition delay of oxathiaphospholanes makes them excellent igniter fuels. Where economy is desirable or high thrust is necessary, the main fuel may be one of relatively low hypergolic activity but possessing high thrust. Examples of these fuels are turpentines and cracked naphthas. These fuels are relatively non-hypergolic at very low atmospheric temperatures. However, once the combustion chamber of the rocket motor has been heated by the reaction of an oxidizer and a fuel, these relatively non-hypergolic fuels are able to maintain the reaction in the combustion chamber. The reaction is begun by passing into the combustion chamber an igniter fuel which is readily hypergolic at very low atmospheric temperatures. The igniter fuel and the oxidizer react to generate a large volume of those gaseous decomposition products which heat rapidly the combustion chamber. The main fuel is then injected into the hot combustion chamber and reacts under these conditions with the oxidizer to continue the gas generation. The flight of the missile is then determined by the thrust characteristics of the main fuel and the oxidizer. For example, in a small size ground-to-air missile only about a pint of igniter fuel is necessary.

It is to be understood that the fuel and the oxidizer must be contacted in a ratio suflicient to initiate the hypergolic reaction, and the ratio of fuel to oxidizer must be regulated at such a point to maintain the hypergolic reaction after it has begun. The ratio may vary over a relatively wide range, dependent on the type of fuel, the oxidizer and the initial temperature of contacting.

Thus, having described the invention, what is claimed 1s:

1. A method of propelling a rocket, which method comprises bringing together separately and substantially simultaneously into the combustion chamber of a rocket motor, a nitric acid oxidizer and 2-chloro-l,3,2-oxathiaphospholane and discharging the gaseous decomposition products from said combustion chamber through an exit nozzle, under conditions of temperature and oxidizer/ fuel ratio such that a hypergolic reaction occurs.

2. A method of rocket propulsion, which method comprises bringing together separately and substantially simultaneously into the combustion chamber of said rocket motor a nitric acid oxidizer and a mixed fuel consisting essentially of 2-chloro-1,3,2-oxathiaphospholane, in an amount between about 25 and about volume percent and the remainder a liquid hydrocarbon, and discharging gaseous decomposition products through an exit nozzle, wherein the ratio of oxidizer and fuel is sufficient to initiate and to maintain decomposition of the fuel.

3. The method of claim 2 wherein said hydrocarbon is diisobutylene.

References Cited in the file of this patent UNITED STATES PATENTS 2,573,471 Malina et al Oct. 30, 1951 2,645,657 Rudel et a1. July 14, 1953 2,655,786 Carr Oct. 20, 1953 2,693,483 Tolkmith Nov. 2, 1954 

1. A METHOD OF PROPELLING A ROCKET, WHICH METHOD COMPRISES BRINGING TOGETHER SEPARATELY AND SUBSTANTIALLY SIMULTANEOUSLY INTO THE COMBUSTION CHAMBER OF A ROCKET MOTOR, A NITRIC ACID OXIDIZER AND 2-CHLORO-1,3,2-OXATHIAPHOSPHOLANE AND DISCHARGING THE GASEOUS DECOMPOSITION PRODUCTS FROM SAID COMBUSTION CHAMBER THROUGH AN EXIT 